Diode pumped alkali metal laser systems (DPALS) show promise as efficient, high power density and compact lasers for direct energy applications. DPALS have extremely low quantum defect heating effects that provide an efficiency loss mechanism. Current DPALS systems have a potential for approximately 30% theoretical optical to optical efficiency. This efficiency is due to excited state population equilibration and sweeping of the one excited state due to the excitation beam. The wall plug efficiency (the percentage of optical power out compared to the total system input power) is also decreased by the roughly 50% due to electrical to optical power efficiency of laser diodes, and the loss in the power supply and the pump diode wavelength control system. Although this seems like poor efficiency, it is actually good efficiency for current lasers. Current wall plug efficiencies are on the order of 5-10%.
Although, DPALS show an improvement in efficiency, there are some technology issues with DPALS. Among the issues with these systems include the issue of pumping energy into the narrow line width D2 state and the transfer of energy into the D1 state from which the stimulated emission of energy occurs. Because of the narrowness of the ground state to D2 absorption line, significant technology and expense is necessary to efficiently pump energy into the system. Currently, the cost of the pump laser diodes in these cases will exceed the general cost on the order of $20-100 per watt, excluding the diode driver system. In addition, the problem is complicated by the requirement to collisionally equilibrate the D2 and D1 states with a buffer gas. There are reactivity issues with many of the collision/buffer gases. The result is that the cost and reliability of the DPALS systems are not at sufficient technology level to be offered for sale, in spite of their performance potential.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an effective and efficient alkali metal laser system.